1. Technical Field
The present invention relates to a control device, which is particularly for an industrial robot, detecting a contact with an external environment.
2. Description of Related Art
A robot arm is provided with a force sensor to detect an external force applied to the robot arm. Japanese Laid-open Patent Publication No. 2006-21287 estimates an internal force acting on a force sensor when a robot arm operates without being in contact with an external environment. When a robot arm is in contact with an external environment, a contact force is determined as a variation obtained by subtracting an estimated value of the internal force from the output of the force sensor. Whether the robot arm is in contact with an external environment or not is determined based on the variation. When the robot arm is in contact with an external environment, the robot arm is made to avoid being in contact with the external environment or to stop, thereby to ensure safe operation of the robot safely.
Incidentally, FIG. 4A is a drawing illustrating relationship between a robot in one attitude and a umbilical member. As illustrated in FIG. 4A, umbilical members 109 suspended from a ceiling are attached at a plurality of points on a robot arm 101 of a robot 1 by a fixing tool 108. In some cases, as illustrated in FIG. 4B, the robot arm 101 operates in such a manner to change its attitude.
When the robot arm 101 operates in such a manner to change its attitude, a force due to pulling of the umbilical member 109 attached to the robot arm 101 or the like is generated. A force sensor 103 attached at a lower portion of the robot 1 detects such a force caused by pulling of the umbilical member 109. Since, usually, the umbilical member 109 is attached depending on the details of a robot system, the type and the number of the umbilical members 109 vary for each robot system. For this reason, unlike an internal force which can be estimated by the configuration of the robot arm 101, a force caused by pulling of the umbilical member 109 cannot be estimated beforehand.
Therefore, whether a robot arm is in contact with an external environment or not cannot be precisely determined since a force caused by pulling of the umbilical member 109 cannot be included in the internal force to be estimated. For this reason, in some cases, even when the robot arm 101 is not in contact with an external environment, it is determined that the robot arm 101 is in contact with an external environment; alternatively, even when the robot arm 101 is in contact with an external environment, it is determined that the robot arm 101 is not in contact with an external environment.
Therefore, a force caused by pulling of the umbilical member 109 needs to be corrected, and the following method is thus considered. First, a real space is divided into a plurality of small regions, and then, for each of the divided small regions, the above-mentioned force when the tip of the robot arm 101 is included in the small region is measured to be stored as a force correction amount. Then, an estimated value of an internal force and a force correction amount corresponding to a region including the current position of the tip of the robot arm 101 are subtracted from an output of a force sensor to determine a deviation as a contact force.
However, if the attitude of the robot arm 101 is changed even when the position of the tip of the robot arm 101 is in the same region, the force correction amount may be inappropriate. For example, the positions of the tip of the robot arm 101 in FIG. 4A and FIG. 4B are the same. However, the angles of each joint of the robot in FIG. 4A and FIG. 4B are different from each other, and thus the attitudes of the robot are different from each other in FIG. 4A and FIG. 4B.
Therefore, in FIG. 4A and FIG. 4B, the magnitudes and the directions of forces of the robot arm 101 for pulling the umbilical member are different from each other. In such a case, the difference in the magnitude and the direction of the above-mentioned force cannot be corrected even when a force correction amount is determined depending on only the position of the tip of the robot arm 101.
The present invention has been made under such circumstances, and an object of the present invention is to provide a robot control device which can highly precisely detect a contact with an external environment without, even in cases in which a force is generated when a umbilical member attached to a robot arm or the like is pulled, being affected by such a force.